Cationic bactericides have potent bacteriostatic ability and high plaque formation inhibitory activity because of their excellent adsorbability onto tissues, and are hence useful for the treatment and prevention of oral diseases such as periodontitis, tooth decay, and halitosis. However, because of their cationic nature, cationic bactericides when used in combination with anionic ingredients, e.g., anionic thickeners or surfactants, may react with the anionic ingredients to lose their bactericidal activity. In order to avoid this inactivation of cationic bactericides, oral compositions employing a combination of a cationic bactericide and a nonionic thickener were proposed (see, JP-A-2-223511 (corresponding to EP 0 368 130) and JP-A-3-127718 (corresponding to EP 0 422 803)). (The term "JP-A" as used herein means an "unexamined published Japanese patent application".) However, since the compositions disclosed in these references are ordinary dentifrices and are mostly rinsed away by mouth washing after use, the pharmaceutical preparation not remaining adsorbed on oral tissues is removed.
For improving the effectiveness of such a drug, measures in enhancing the adhesive properties of a preparation itself were proposed. A generally employed technique for improving the adhesion of a preparation to wet surfaces, e.g., the mucous membrane in the oral cavity, is to incorporate a carboxyvinyl polymer, polyacrylic acid, or an analogue thereof, which each shows excellent adhesion to the mucous membrane in the oral cavity. Examples of such preparations include solid preparations for oral use and the high-viscosity gel containing a carboxyvinyl polymer and a hydroxypropyl methyl cellulose in combination as proposed by the present inventors (see JP-A-7-267839). However, these conventional preparations still have the problem that the cationic bactericide may lose its bactericidal activity when used in combination with an anionic ingredient, e.g., a carboxyvinyl polymer. Furthermore, solid preparations and high-viscosity gels have poor spreadability and are less apt to evenly spread over the whole surfaces of the oral cavity.
On the other hand, liquid oral compositions proposed so far include an aqueous gel for oral cavity containing a hydroxypropyl methyl cellulose, in which hydroxyl groups have been converted to hydrophobic groups, and having high thixotropic properties (see JP-A-6-100424) and a liquid dentifrice containing an abrasive material and hence having enhanced long-term stability (see JP-A-4-210908). Furthermore, sprayable compositions where gel-forming cellulosic polymer was compounded therein were proposed (see EP 0 679 390). However, no oral composition has been suggested which contains a cationic bactericide as the active ingredient and is satisfactory in stability, ease of administration, and adhesive property.